1. Field of the Invention(s)
The present invention(s) generally relate to wireless receivers. More particularly, the invention(s) relate to systems and methods for combining signals from multiple active wireless receivers.
2. Description of Related Art
In microwave radio systems, receiver protection (backup) systems are common. In a typical receiver protection system, there is one main active receiver and one or more other secondary “backup” receivers. The secondary protection receivers are not actively receiving while the main active receiver receives signals from a wireless source (e.g., a tower or other wireless signal transmitting device). If the main active receiver fails or is operating below an acceptable limit, the main active receiver may be switched such that the main active receiver is no longer actively receiving and one of the secondary standby protection receivers become the main receiver. In the prior art, there is only one receiver actively receiving at any one time.
Space diversity configuration has not been changed in decades. FIG. 1 and FIG. 2 depict today's two most commonly used 1+1 configurations in the prior art. FIG. 1 depicts a main active receiving radio frequency unit (RFU) 102 and a secondary protection RFU 102 in the prior art. In FIG. 1, a main active receiving unit 102 in an environment 100 receives a wireless signal from a wireless communication tower 106 (e.g., cell tower or other microwave radio device) via an antenna. If the main active receiving unit 102 fails or falls below an acceptable level of performance, the main active receiving unit 102 may go into standby mode and the secondary protection receiving unit 104 may begin to actively receive, thereby receiving the signal from the wireless communication tower 106.
FIG. 2 depicts a main active receiving radio frequency unit (RFU) 202 and a secondary protection RFU 204 when an RFU enclosure is optimized for protection in the prior art. In an environment 200, a main active receiving unit 202 and a secondary protection receiving unit 204 receive the signal from one antenna (i.e., wireless communication tower 206). For example, an antenna receives a wireless signal from the wireless communication tower 106 and provides the signal to a filter and/or diplexer. The filter and/or diplexer provide the signal to the main active receiving radio frequency unit 202. A coupler provides the signal to the secondary protection receiving radio frequency unit 204 as well, however, like the protection receiving unit in FIG. 1, the secondary protection receiving radio frequency unit 204 is typically not actively receiving. If the main active receiving unit 202 fails or falls below an acceptable level of performance, the main active receiving unit 202 may go into standby mode (i.e., the main active receiving unit 202 may stop actively receiving) and the secondary protection receiving unit 204 may actively receive. As a result, the secondary protection receiving unit 204 may receive the signal from the wireless communication tower 106.
In both configurations of FIGS. 1 and 2, two receivers are on all the time, however, the systems may decide to use either the main active receiving unit or the secondary protection receiving unit. The determination to switch to a receiving radio frequency unit may be based on a quality alarm of each channel such as slope alarm, equalization alarm, or RSL (receiver signal level) low alarm. In legacy implementations, this decision may occur in real time either on a bit-by-bit or data block by data block basis.
Unfortunately, when the system switches receivers, performance suffers (e.g., the system may no longer be hitless). Today's 1+1 architecture only achieves hitless switching protection during multi-path fading conditions. Further, other failure mechanisms, including equipment failure, generally affect the performance (e.g. the system is not hitless)”.